Several forms of surface chemistry and surface treatment depend upon the interaction of a substrate with its environment, including annealing, drying, and exposure to reactive gas. For example, Atomic Layer Deposition (ALD) is a high-quality thin-film deposition technique based on sequential, self-limiting surface reactions. Atomic layer deposition works by exposing a substrate sequentially to two or more reactant vapors or solutions and maintaining the substrate temperature within, for example, a temperature range that depends on the chemistry of the particular ALD reaction. A typical ALD process involves a sequence of two different and alternating surface reactions involving two different gaseous reactants referred to herein as A and B. The ALD system is typically purged of reactant gas in between reactions with a non-reactive purge gas C, and/or is pumped clean of the reactant gases. Sequencing the reactions provides precision in the rate of deposition and allows the use of highly reactive reactants. With each reactant exposure, a self-limiting reaction occurs on the surface of the substrate if the substrate temperature is, for example, within the right temperature range, or alternative energy sources are provided, such as energetic ions or molecules or atoms, ozone, plasma, UV light, etc.
ALD can control the thickness of deposited films at the level of an atomic or sub-atomic layer. Thus films deposited by ALD tend to be uniform over large areas. In addition ALD allows deposition of conformal films on structures having very high aspect ratios (e.g., >>10). A wide variety of materials may be deposited by ALD, including semiconductors, metals, oxides, nitrides, and other materials. ALD techniques can thus deposit thin films one atomic layer at a time, in a “digital” fashion. Such “digital” build-up of material greatly simplifies thickness control, thus reducing both the complexity and cost of thin film deposition.
Many industries, such as the optoelectronics industry, can benefit from the high uniformity, high aspect ratio conformal coating abilities and low cost of ALD. Unfortunately, prior art ALD systems have mostly been made for semiconductor wafer processing, which is oriented to batch processed wafer handling systems. Although existing ALD systems are suitable for the semiconductor industry, they are unsuitable for high volume manufacturing of large area devices such as photovoltaic cells. Current systems are typically designed to coat small area wafers. Scaling up systems that coat a small area at a time might not be practical for coating large area sheets, panels or rolls of material. ALD may be too slow and expensive overall, if only small area batch processing can be performed. Further, surface treatments such as annealing, drying, and exposure to reactive gases cannot be carried out at high-volume for large-area substrates when the surface treatments and/or reactions take place in a relatively smaller treatment chamber.
Thus, there is a need in the art, for a high throughput surface treatment method and system.